Des Moines, Iowa ? Iowa Gov. Tom Vilsack, Kansas Gov. Kathleen Sebelius and nine other top executives from beef-producing states have sent a letter to U.S. Agriculture Secretary Ann Veneman asking for regular briefings on steps being taken to safeguard the nation’s meat supply against mad cow disease.

“We will continue to work together as states to put protocols in place to ensure the safety of our nation’s beef supply,” Vilsack said.

The first U.S. case of mad cow disease surfaced in a Washington state dairy cow slaughtered Dec. 9. The Holstein was a “downer” cow, meaning it could not stand on its own.

Veneman on Tuesday ordered changes in processing methods to ensure that beef is not contaminated with brain, spine or nerve tissue that can spread mad cow disease. Cows that cannot stand on their own no longer will be accepted for slaughter. Cows tested for mad cow will not be processed until results are known.

Other governors signing the letter were: Mike Johanns of Nebraska; Bill Owens of Colorado; Tim Pawlenty of Minnesota; Bob Holden of Missouri; Judy Martz of Montana; John Hoeven of North Dakota; Brad Henry of Oklahoma; Mike Rounds of South Dakota and Rick Perry of Texas.